K for C looks gimmicky to me (unless, as BBH mentions, it's known to me as a
German form - is
Kaleb used in Germany??). A sampling of the sort of gimmickiness I'm talking about: Keystone Kops, Krispy Kreme, Kleenex (for the sound of the word "clean"), Kool-Aid, Kwik Kopy... you get the idea. If I were
Caleb I would want it spelled with a C because I think it's just likely to give a more dignified impression.